Aluminium base alloys and anodes

ABSTRACT

Aluminum base alloys which are suitable for use in the as cast state as galvanic anodes, the alloys comprising 1-15% zinc, 0.005-0.1% indium and 0.4-10% magnesium, the balance being aluminum of at least 99.8 percent purity with inconsequential impurities. The alloy may optionally include some tin, for example in the range of 0.1-0.5 percent, some gallium in the range of from 0.005 to 0.017 percent and a grain refiner such as titanium and zirconium.

United States Patent Inventor Trevor Broughton Beaconsfield, England Nov. 25, 1968 Oct. 26, 1971 The British Aluminium Company Limited London, England Appl. No. Filed Patented Assignee ALUMINUM BASE ALLOYS AND ANODES lieierences Cited UNITED STATES PATENTS Primary Examiner-Richard 0. Dean Attorney- Peck & Peck ABSTRACT: Aluminum base alloys which are suitable for use in the as cast state as galvanic anodes, the alloys comprising l-l5% zinc, 0.005-0. 1% indium and 04-10% magnesium, the balance being aluminum of at least 99.8 percent purity with inconsequential impurities. The alloy may optionally include some tin, for example in the range of 0.1-0.5 percent, some gallium in the range of from 0.005 to 0.017 percent and a grain refiner such as titanium and zirconium.

1 2 ALQMINUM BA SE AIILQYS i The melt was then thoroughly stirred with the temperature BACKGROUND OF THE INVENTION controlled between 710730 C.

Casting was then carried out into dies held at l250 C. The requltemehts for galvanic anodes are a g operating Half inch sections were cut from I inch-diameter test bars potential and a high efficiency measured as electrical output 5 of the material to be tested and electrical connections made P Unit mass Ofmetal Consumedthrough a threaded length of %-inch diameter aluminum rod y conventional alloys used for forming anodes, for screwed into the upper machine surface of the specimen. Both ample aluminum-zinc-tin alloys production at the present machined surfaces were marked ofi" using a topping off medi.

time require a heat treatment after being cast before y are um and the weighed samples were then mounted concentrisuitable for use. There are considerable economic and technil0 ll i 9.l l di 12-in h high, shot-blasted mild steel c l n age in ing le to produce h gh p y fidrums containing about 11 liters of natural sea water. Gentle 'cial anodes which will operate satisfactorily in the as-cast conagitation by stirring was used during the test and the elecditioh Without the necessity for formal heat tl'eatmehttrolyte in the tank was changed regularly. The tests were car- BRIEF SUMMARY OF THE INVENTION We have found that the incorporation of magnesium in an aluminium-zinc-indium alloy in the correct proportion provides a satisfactory as-cast product.

Accordingly the invention provides in one aspect an aluminum base alloy comprising 1-15 percent zinc, 0.005-0.1 percent indium and 0.4- percent magnesium, the balance being aluminum of at least 99.8 percent purity with inconsequential impurities.

The proportion as impurities of silicon and iron should each ried out at laboratory temperatures.

The current supplied by the dissolving anode after being connected to the steel drum was restricted to an anode current density of 10 ma./in. by means of a variable resistor in the external circuit. The potential drop across a further accurately calibrated resistor (also in the external circuit) was used to monitor the current flow and these values were recorded automatically every four hours during test. The total current supplied by the anode section could therefore be calculated.

The period of testing varied from 40-60 days by which time about 50 percent of the specimen had been consumed. After Preferably be belw Percent Preferably the Zmc content 15 removing from the test environment specimens were cleaned between 2 and 10 Percent and with advantage between 25 in 1:1 nitric acid (to remove adherent corrosion product,) and and 8 percent. Preferably the indium content is between were h i h d after d i 0.014105 Percent and with advantage between and The theoretical output for the particular weight loss of the percent. Preferably the magnesium content is between 0.4 and im n was al ulated u ing an electrochemical equivalent 1 percent n with advantage is between and Percent for the particular alloy on test (i.e. allowance made for the p r icula y Whe r st ns t incendlve p i g pp yzinc content of the alloy) and the efficiency calculated as the The alloy may also include some tim, for example in the range percentage f the theoretical output actually supplied by the l0.l percent to 0.5 percent. anode during testing.

It is preferable to include some gallium in the range 0.005 to Potentials were measured at regular intervals throughout 0.017 percent and preferably for example 001 percent. the test using a saturated calomel electrode in contact with the In this specification all percentages are by weight. dissolving aluminum anode or on the outside of any adherent It is further preferred to include a grain refiner of any suitacorrosion present on the specimen surface- The al e o Ible form (for example titanium and zirconium) to improve the potential quoted is that measured on the final day of the test. cast product. Examples of specifications of and properties of anodes In another aspect the invention provides an anode in the asmade from alloys in accordance with the invention are shown tcast state made from an alloy as set out above. n in table 1.

. TABLE} Operatln potentla at 10 Ina/in. Composition Efliclsney (mv. versus at 10 saturated Base ma./in. calomel purity Magnesium Zinc percent electrode) 99.8 0. a. 52 1,110 99.8 0. 78 3. 64 92 1,120 99.8 0.64 6. 01 l, 99.3 0. 62 2. 51 91 1,100 99.8 0. 60 3.55 91 1,100 99.8 0.62 3554 89 1,110 99. 8 0.67 3. 51 35 1,100 99.8 0. 99 a. 95 at 1,080 99.8 0. 36 3.67 85 1, 000 nEscRiFTioN OF THE PREFERRED EMBODIMENTS It will be noticed that in the case of composition 1 where the magnesium content is below 0.4 percent the operating potential fell to l,000 mv. and the resulting anode was less satisfactory than those of higher magnesium contents.

Further examples of specifications of and properties of anodes made from alloys in accordance with the invention are shown in table 11. In these examples, the copper content was in Some aluminum base anodes were made up and tested by 60 way of example as follows:

Aluminum was melted and raised to a temperature of 710 C. Zinc, indium, (and in some cases tin) were added as required and this operation was followed by degassing. Magnesium was then added as required and to minimize oxidation 65 each case found to be less than 0.005 percent and the silicon effects additions were made under a layer of Coverall 33F. and iron contents are shown. A

'7 TABLE II Potential at 10 miL/in. mv. Percent composition I Emclency at (versus satul 10 ma./in., rated calomel Alloy designation Mg 81 Fe Zn 'In a percent electrode) 0. 69 0.10 0.06 3. 54 0. 032 0 012 90 1 0. 70 0.114 0. 10 3. 55 0.033 0 012 86 1, 110 0. 70 0. 04 0. 03 3. 52 0. 030 0 011 93 1, 110 0. 72 0. 17 0. 08 7. '53 0. 03 0 012 88 1, 076 0. 68 0. 04 0. 04 3:56 0. 03 0 011 87 l, 0. 71 0. 08 0. 06 4. 69 0. 034 0 012 84 1, 100

1 Balance A101 99.8% urity.

The applicants have investigated the effect of variations in casting techniques on the electrochemical properties of alloys according to the invention. These investigations involved variations in the liquid metal temperature, variations in the mould temperature and variations in the cooling technique.

Three cooling techniques were tried, one of these identified as the standard procedure involved casting the metal into a mold and, when it had become sufficiently solidified, removing it from the mold and allowing it to cool, the second technique identified as water quench-cold water involved casting the metal into a mold and, when it had become sufficiently solidified, removing it from the mold and quenching it in cold water, and the third technique identified as very slow cool in molds involved casting the metal into a mold and allowing it to cool in the mold to ambient temperature. This latter technique gave a retarded rate of cooling and a superior result as can be seen from table 11! below. The alloy used for the investigation of which the results results are given in table 11]; was an alloy containing 0.68 percent magnesium, 4.01 percent zinc, 0.038 percent indium, 0.012 percent gallium, 0.12 percent silicon, 0.07 percent iron and less than 0.005 percent copper.

moulds.

The addition of grain refining elements such as Zirconium ;and titanium to alloys according to the invention was investigated and the results are shown in table 1V below. These results indicate that beneficial results are obtained with the addition of a grain refining element, preferably titanium in the range of from 0.005 to 0.07 percent and more specifically in the range from 0.01 to 0.04 percent. ln each of the alloys shown in table IV the copper content was less than 0.01 percent.

2. An aluminum base alloy according to claim 1 containing less than 0.2 percent of each of silicon and iron as impurities.

3. An aluminum base alloy according to claim 1 in which the zinc content is not less than 2 percent and not more than 10 percent.

4. An aluminum base alloy according to claim 3 in which the zinc content is not less than 2.5 percent and not more than 8 percent. I

5. An aluminum base alloy according to claim 1 in which the indium content is not less than 0.01 percent and not more than 0.05 percent.

6. An aluminum base alloy according to claim 5 in which the indium content is not less than 0.03 percent and not more than 0.04 percent.

7. An aluminum base alloy base according to claim 1 in which the magnesium content is not less than 0.4 percent and not more than 1 percent.

8. An aluminum base alloy according to claim 7 in which the magnesium content is not less than 0.06 percent and not more than 0.8 percent.

9. An aluminum base alloy according to claim 1 in which the tin content is in the range of from 0.1 to 0.5 percent.

10. An aluminum base alloy according to claim 1 in which the gallium content in the range of from 0.005 to 0.017 percent.

11. An aluminum base alloy according to claim 10 in which the gallium content is 0.01 percent.

12. An aluminum base alloy according to claim 1 including, as a grain refiner, titanium in the range of from 0.05 to 0.07 percent.

13. An aluminum base alloy according to claim 12 containing not less than 0.01 percent and not more than 0.04 percent titanium.

14. A method of producing a galvanic anode comprising forming an aluminum base alloy consisting essentially of 1-15 percent zinc, 0.005-0.1 percent indium, 0.4-10 percent magnesium, 00.5 percent tin and 0-0.017 percent gallium, the balance being aluminum of at least 99.8 percent purity with inconsequential impurities, casting the alloy into a mold and allowing it to cool in the mold to ambient temperature.

15. A method according to claim 14 in which the alloy includes, a a grain refiner, titanium in the range of from 0.005 to 0.07 percent.

16. A cast galvanic anode composed of an aluminum base v ailoy consisting essentially of 1-15 percent zinc, 0.005-0.1

TABLE IV Potential at 10 max/in. Efilciency -mv. Percent composition 1 at 10 (versus sstma./in. urated calo- Mg S1 Fe In Ga Zn T1 percent mel electrode) 74 0. 08 0. 06 0. 031 0. 01 3.75 01 1,110 0.71 0. 09 0. 06 0. 030 0. 013 3. 82 005 87 1, 100 0. 69 0.09 0. 06 0.034 0. 01 3. 79 01 85 1, 120 0:438 0.08 0. 07 0.036 0. 01 3. 79 0. 02 94 1, 120 0.73 0.08 0. 06 0. 034 0. 012 3. 81 0. 015 85 1, 100 0. 63 0.07 0. 06 0. 037 0. 01 3. 75 0. 02 83 l, 100 0.09 0. 07 0. 06 0.034 0. 012 3. 86 0. 020 93 1, 110 0.66 0.07 0. 07 0. 005 0 01 3. 81 0. 02 81 l, 100 0.70 0. 08 0. 07 0. 035 0. 013 3.80 0. 02 91 1, 090 0. 64 0.08 0. 08 0. 037 0. 01 3. 81 0. 02 95 1. LBalance 1A1 01 993% purity.

percent indium, 0.4-1 0 percent magnesium, 0-0.5 percent tin and 0-0.017 percent gallium, the balance being aluminum of 5 at least 99.8 percent purity with inconsequential impurities,

said anode having been cast in a mold and allowed to cool therein to ambient temperature.

* t tlr 

2. An aluminum base alloy according to claim 1 containing less than 0.2 percent of each of silicon and iron as impurities.
 3. An aluminum base alloy according to claim 1 in which the zinc content is not less than 2 percent and not more than 10 percent.
 4. An aluminum base alloy according to claim 3 in which the zinc content is not less than 2.5 percent and not more than 8 percent.
 5. An aluminum base alloy according to claim 1 in which the indium content is not less than 0.01 percent and not more than 0.05 percent.
 6. An aluminum base alloy according to claim 5 in which the indium content is not less than 0.03 percent and not more than 0.04 percent.
 7. An aluminum base alloy according to claim 1 in which the magnesium content is not less than 0.4 percent and not more than 1 percent.
 8. An aluminum base alloy according to claim 7 in which the magnesium content is not less than 0.6 percent and not more than 0.8 percent.
 9. An aluminum base alloy according to claim 1 in which the tin content is in the range of from 0.1 to 0.5 percent.
 10. An aluminum base alloy according to claim 1 in which the gallium content in the range of from 0.005 to 0.017 percent.
 11. An aluminum base alloy according to claim 10 in which the gallium content is 0.01 percent.
 12. An aluminum base alloy according to claim 1 including, as a grain refiner, titanium in the range of from 0.05 to 0.07 percent.
 13. An aluminum base alloy according to claim 12 containing not less than 0.01 percent and not more than 0.04 percent titanium.
 14. A method of producing a galvanic anode comprising forming an alluminium base alloy consisting essentially of 1-15 percent zinc, 0.005-0.1 percent indium, 0.4-10 percent magnesium, 0-0.5 percent tin and 0-0.017 percent gallium, the balance being aluminum of at least 99.8 percent purity with inconsequential impurities, casting the alloy into a mold and allowing it to cool in the mold to ambient temperature.
 15. A method according to claim 14, in which the alloy includes, as a grain refiner, titanium in the range of from 0.005 to 0.07 percent.
 16. A cast galvanic anode composed of an aluminum base alloy consisting essentially of 1-15 percent zinc, 0.005-0.1 percent indium, 0.4-10 percent magnesium, 0-0.5 percent tin and 0-0.017 percent gallium, the balance being aluminum of at least 99.8 percent purity with inconsequential impurities, said anode having been cast in a mold and allowed to cool therein to ambient temperature. 